Change iteration order to avoid temporary map

src/arena_allocator.hpp

@@ -9,6 +9,7 @@
 #include <iostream>
 #include <limits>
 #include <new>
+#include <span>
 #include <type_traits>
 #include <typeinfo>
 #include <utility>
@@ -639,6 +640,12 @@ template <typename T> struct ArenaVector {
 
   void clear() { size_ = 0; }
 
+  // Implicit conversion to std::span
+  operator std::span<T>() { return std::span<T>(data_, size_); }
+  operator std::span<const T>() const {
+    return std::span<const T>(data_, size_);
+  }
+
   // Iterator support for range-based for loops
   T *begin() { return data_; }
   const T *begin() const { return data_; }